The jury began its deliberations Monday in the copyright phase of Oracle’s lawsuit against Google over Android.

Attorneys for both sides made their closing arguments Monday morning, and the jury left the courtroom to consider its verdict at about noon West Coast time. It’s unlikely the jurors will reach a decision before Tuesday, and it’s possible they will take several days after that.

For Oracle to win, all 12 jurors must agree that Oracle proved its case by a “preponderance of the evidence,” or by most of the evidence presented at trial.

The trial is in three parts, and this first verdict will be for the copyright phase only. The next phase will address Oracle’s allegations of patent infringement, and the final phase will determine any damages Oracle should receive.

However, Oracle’s copyright claims are seen as the strongest part of its case, so this first verdict is considered crucial by both sides.

Oracle sued Google about two years ago, arguing that its Android software infringes Java patents and copyrights that Oracle acquired when it bought Sun Microsystems. Google denies any wrongdoing, saying it built a “clean room” version of Java.

The judge has instructed the jury that simple names and phrases, such as those given to the methods and classes in Oracle’s Java APIs (application programming interfaces), can’t be copyrighted under U.S. law.

Instead, the jury has to decide whether Google infringed the “structure, organization and sequence” of the Java APIs — in other words, how they are organized and how they relate to each other. If it decides Google did infringe the APIs, it must then decide if Google’s usage is protected by “fair use.”

Robert Van Nest, an attorney for Google, made several fair-use arguments in his closing statement on Monday. One measure of fair use is how significant the copied material is to the original work as a whole, he said.

Google is accused of copying 37 of Oracle’s Java APIs (Java application programming interfaces) in Android, and Van Nest said that represents a small part of Java as a whole.

“The relevant comparison is the structure, sequence and organization of 37 APIs out of the entirety of Java,” he said.

He also argued Google’s use of the APIs was “transformative,” meaning it created something new and different out of the APIs. Android is the first successful Java smartphone platform on the market, Van Nest said.

Oracle attorney Michael Jacobs disagreed, pointing to Research In Motion’s BlackBerry and Danger’s Sidekick. “Is Android kind of cool and is it the hot new thing? Of course it is,” he said. “But is it transformative under the meaning of the law? No.”

The jury must also decide whether Sun’s public statements about Java could have led Google to believe it didn’t need a license to use the technology. Google has repeatedly cited a 2007 blog post from former Sun CEO Jonathan Schwartz congratulating Google on Android’s release.

“Google’s a big company, they know business isn’t done by blog posts,” Jacobs told the jury on Monday.

It’s been a complex case, and Judge William Alsup, who is overseeing the trial, gave the jury 18 pages of instructions to help them make their decision. The form for their verdict has four questions, some divided into multiple parts. (A copy of the instructions and verdict form is here.)

Judge Alsup himself must also make some decisions based on his interpretation of copyright law, including whether Oracle’s APIs can be covered by copyright at all. If he decides they cannot be, the jury’s verdict may still be relevant if Oracle appeals Alsup’s decision to a higher court.

The jury has been required to attend court in this trial from 8 a.m. to 1 p.m., so that’s the time they’ll now spend each day debating their verdict until they reach a decision.

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